A variety of gearboxes or "adaptors" as they are sometimes referred to in the trade, have been provided for driving speedometers or odometers at speeds that reflect the actual speed of or distance traveled by the associated vehicle. Since the internal gearing within speedometers and odometers have become standardized and since drive ratios in the drive train between the vehicle's transmission output shaft and wheels vary from vehicle to vehicle, the adaptor or gearbox is necessary to reflect actual vehicle speed and distance traveled.
One such gearbox includes a split metal housing supporting input gearing which drives intermediate gearing that in turn rotates an output gear so that the direction of rotation of the input gear and the output gear are the same and the intermediate gearing performs an idler function as well as a gear ratio function. The shafts supporting these gears lie in a common plane and for a direction of rotation of the input gear in either direction, it can be shown that the reaction forces of the input gear and the output gear on the intermediate gear are substantially in the same direction on the same side of the common plane. These reaction forces on the intermediate gearing decrease gear train efficiency and require high strength bearings for the intermediate gear, usually a steel bearing. While it may be desirable to construct this prior gear box with a less expensive housing material such as plastic, it is doubtful because of the side loadings on the intermediate gear that such a gear box could be designed without the interposition of heavy duty metal bearings.
It is a primary object of the present invention to ameliorate the problems noted above in prior speedometer adaptors.